To fix that GPG error; in terminal enter:
Now for qmail. If this was my system, I would remove those directories. It looks like a low risk move. But I am fully backed up so if things go south, I can restore. Having never installed qmail I cannot be 100% certain of what will happen. So if you can afford to take a chance, open a terminal and ..
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 06BBDC2602DFE7E7
Then do a search on qmail and remove everything you find.
If your not feeling lucky give this thread a while and see if someone else will comes along that can verify these things about qmail.